pump won't shut off

Our lawn irrigation pump won't shut off. Initially after all the zones ran and the system stopped, the pump would kick on and off about every 15 min. Now after all the zones are finished and turned off, the pump just keeps running. The only way we can turn it off is to disconnect it from the power source. Where do we start with trouble shooting?

I assume that you have a pressure tank and a pressure switch. If that is not the case, come back and tell us what you have.

I assume that you don't have a relay arrangement with your irrigation system, and that it is controlled with a pressure switch.

Is the pump a submersible in a well, a jet pump, or an "irrigator" centrifugal pump? Can you find the model and/or performance data for the pump?

The most likely causes in decreasing likelihood are:
1. Leaky or broken pipe in the irrigation system
2. Ran out of water at the suction of the pump
3. Lost prime at the pump (caused by loss of water or leak in suction pipe). Doesn't apply to submersible pump.
4. Pump failure
5. Pressure switch failure

You need a pressure gauge connected to the same part of the system as the pressure switch. If you don't have a gauge, turn off the pump power and procure and install a gauge. You can get the kind that connects to a hose outlet, if there is a hose connection near the pressure switch. If no hose connection available, then you need to add a hose connection or get a gauge with 1/4" pipe thread (which is about 1/2" if you measure it with a ruler) and a reducer or other fittings necessary to connect the gauge. You should get a 0-100 psi gauge, 0-160 or 0-60 if the 0-100 is not available.

You may need a tire gauge and bicycle pump or compressor to adjust air in the tank, but that is not critical to the diagnosis of the "pump won't stop" problem.

It will be a great help to isloate the problem if there is a valve at the outlet from the pressure tank to the system, so you can operate the pump without any connection to the underground piping. That will allow you to rule out or rule in one of the more difficult to find problems. If you don't have one, try to add it while working on the pressure gauge. If that is not practical, we can work on it without the valve. Plastic PVC ball valves are available at HD with both threaded and socket connections. Threaded brass gate valves are also available.

You can check to see if the pressure switch is closed. It would be a miracle if it is not, since the pump is running. Take the cover off the pressure switch (with the power off) and observe the contacts to see if they are touching (closed) or open. Use a flat bladed screwdriver to pry up the plate at the bottom of the switch. You should hear it click OFF and see the contacts open. It may or may not click ON when you release the plate. If the pressure is low, it should click ON.

Tell us what the pressure gauge is reading with the pump running. Does the pump turn off when the valve to the irrigation system is closed?

Then turn the pump off an observe the pressure gauge. With all water uses off, does the pressure drop quickly? That could indicate a leak in the lines somewhere.

Report back on findings and observations and we will try to help with the diagnosis.